I've recently gone through the DAL interview process twice. First time, the cog test got me. Fortunately, I was invited back for a second interview and was successful.

I used several interview prep companies to get ready for the big day(s). Of course, not all are the same quality in my opinion. One gentleman that was suggested for DAL prep was terrible and it was clear he just wanted the money and provide no help whatsoever compared with the others. He actually used to be on the interview panel until he realized the money he could make doing prep. Another gentleman who also used to sit in on panel interviews spent HOURS with me over the phone and video chat. Spectacular in my opinion.

Please feel free to PM me if you'd like my opinion on the services worth the time and money.